// console.log(a);//输出undefined
// var a = 1;

//变量提升 
//预编译后  ：

// var a;  
//console.log(a)
//a = 1;

function fn(a) {
    console.log(a);
    var a = 123;
    console.log(a);
    function a() { }
    var b=function(){ }
    console.log(b);
    function d() { }
    var d =a
    console.log(d);
}
fn(1)